Existing electronic systems, such as for example telephone switches or processing equipment, are often assembled from numerous functional electronic modules slidably mounted in a casing, typically comprising at least one shelf that mounts in a bay. Such casings must typically be shielded to limit electromagnetic emissions from the modules and the connectors to the modules. Numerous shielded shelving assemblies, such as those disclosed in U.S. Pat. Nos. 4,631,641 and 5,539,620, are known.
The shelving assembly disclosed in U.S. Pat. No. 4,631,641, for example encloses an entire shelf of electronic modules between top, bottom, side and rear walls. The numerous adjacent front faceplates of the modules complete the enclosure. Top and bottom walls are meshed and allow for airflow across the modules, while still shielding electronic emission. However, for electronic modules working at higher frequencies, openings in any enclosure may permit the emission of electromagnetic interference ("EMI").
U.S. Pat. No. 5,539,620 discloses individually shielded modules each encapsulating a plurality of circuit boards, and mountable within a shelf.
Existing high speed synchronous optical network transport nodes are made up of many high speed electronic functional modules having electronic components operating at frequencies between 2.5 and 10 GHz. Each module contains at least one printed circuit board (PCB). Each PCB is individually housed in a sealed enclosure thereby forming an EMI contained module. An electrically conductive bulkhead extends from the front of each module, and provides a front EMI shield for the module, while permitting securement of the module in the shelf. Heat is transferred from the enclosed PCB through the enclosure. The remainder of the enclosure is made of a thermally conducting material such as aluminum, and has a number of cooling fins. These fins facilitate heat transfer and direct air flow provided by a forced air cooling system between adjacent enclosures mounted within a shelf. Each PCB has a connector extending from an end of its enclosure. The connector is suited to engage a mating connector on the backplane of the shelf. To provide an EMI seal, the PCB enclosure also engages an electrically conductive gasket surrounding the connector on the backplane. The gasket provides EMI containment at the backplane.
Such opto-electronic systems are typically provided in many different configurations often without a full complement of functional transport cards. A typical shelf has ten mounting slots. Depending upon the configuration, between two and eight slots can be left unused. Leaving these unused slots empty, creates a number of problems. Specifically, unused connectors at the backplane will emit EMI; and airflow within the rack will be disrupted by an empty slot. Moreover, some system designs require some basic electronic terminating connections to the backplane.
These problems are presently addressed by providing a full sized, functional transport module as a filler module. Often the electronics carried by the PCB of a filler module are simplified to provide only the minimum required functionality. This, however, is quite costly as a full sized EMI housing is made almost entirely of cast aluminum.
The present invention attempts to address some of the shortcomings of existing filler modules.